I have 2 flat cot bedsprings, one at each end, with bed
side rails making the top side edges between the two.They
stand on end. There is fence wire top between the bed side
rails. Makes an arbor trellis. It is not welded, but put
together with wire. It is not the head and foot
boards but the springs. There are the green metal fence posts
driven into the ground on the 4 corners to hold it up- wired---
It stood up even through Hurricanes Ivan and Dennis.
about 8 years now.
Sorry no picture....

I have a seven sister rose bush on a metal headboard and it has held up thru three floods. Also have a clematis growning up a metal headboard and that has been thru two floods and never wavered. I have a wisteria climbing over a 1/2 inch pcv pipe that is arched and that has also gone thru a couple of floods. As long as you stake them into the ground good they should last almost forever.

Thanks for the replies. I will have to just play around with the idea and do some more research.
Clare